This invention relates to spool valves and, in particular, to spool valves for marine stern drives.
Spool valves conventionally include an outer member or housing having a longitudinal bore extending therethrough. A spool is reciprocatingly received in the bore. The interior of the bore has one or more circumferential grooves, while the exterior of the spool also has one are more circumferential grooves. The grooves in the spool are aligned with the grooves in the bore of the outer member, or are nonaligned with the grooves in the outer member, depending upon the axial position of the spool relative to the bore.
When one of the grooves in the spool becomes aligned with one of the grooves in the bore, the fluid is immediately presented with a relatively large area for communication between the outer member and the spool. Thus a rush of fluid between the outer member and the spool may immediately occur. For some applications this proves to be disadvantageous. For example, when such spool valves are used for steering cylinders on inboard/outboard, outboard or inboard marine drives, this characteristic of typical spool valves presents problems. Some marine stem drives are prone to side to side movement and this characteristic is exacerbated by the use of such a spool valve which immediately applies full fluid pressure as one of the grooves in the spool becomes aligned with one of the grooves on the housing.
In one particular type of steering cylinder, the exterior of the cylinder acts as the spool for a spool valve. The housing extends about the exterior of the cylinder for relative axial movement between the housing and the exterior of the cylinder. In this case the size of the valve spool is effectively fixed and thus the volume of fluid which flows as the valve opens cannot be controlled by reducing the size of the valve spool.
Accordingly, it is an object of the invention to provide an improved spool valve where the flow of fluid through the valve is limited compared to a conventional spool valve having annular grooves on both the spool and the housing.
It is another object of the invention to provide an improved spool valve where the initial flow of fluid through the valve is reduced, when the valve initially opens, compared to the flow through the valve when the valve is fully opened.
Is a further object of the invention to provide an improved combination actuator and spool valve, where the actuator housing acts as the spool for the spool valve, and where the flow through the spool valve is controlled compared to a conventional spool valve having annular grooves on both the spool and the housing.
It is a still further object of the invention to provide an improved marine steering apparatus where drive induced oscillations are dampened compared to a similar unit using a conventional spool valve to control fluid flow to and from the steering cylinder, without the need for a centering spring, an external damper or chamfers on conventional spool grooves to create a leak path.
According to one aspect of the invention, there is provided a valve comprising a housing with an elongated bore having a longitudinal axis and a spool reciprocatingly mounted within the bore for relative movement of the housing along the spool parallel to the axis. The housing has a housing passageway and the spool has a spool passageway. The passageways align in at least one axial position of the spool along the bore, whereby fluids can pass between the spool and the housing. The passageway of one of the spool or the housing includes a first groove which extends parallel to the axis, but not completely, circumferentially about said one of the spool or the housing. The passageway of another of the spool or the housing includes a second groove which extends circumferentially about said another of the spool or the housing.
According to another aspect of the invention, there is provided a combination actuator and spool valve. The actuator has an actuator housing with an outer portion which forms a spool for the spool valve. The spool valve has a valve housing which is generally concentric with the actuator housing and extends about the actuator housing. The valve housing has an elongated bore with a longitudinal axis and the spool is reciprocatingly mounted within the bore for relative movement of the housing along the spool parallel to the axis. The valve housing has a housing passageway and the spool has a spool passageway. The passageways align in at least one axial position of the spool along the bore, whereby fluids can pass between the spool and the valve housing. The passageway of one of the spool or the valve housing includes a first groove which extends parallel to the axis, but not completely, circumferentially about said one of the spool or the valve housing. The passageway of another of the spool or the valve housing includes a second groove which extends circumferentially about said another of the spool or the valve housing.
According to a further aspect of the invention, there is provided a marine steering apparatus comprising a tiller connected to a combination actuator and spool valve mounted thereon. The spool valve has a valve housing which is generally concentric with the actuator housing and extends about the actuator housing. The valve housing has an elongated bore with a longitudinal axis and the spool is reciprocatingly mounted within the bore for relative movement of the housing along the spool parallel to the axis. The valve housing has a housing passageway and the spool has a spool passageway, the passageways align in at least one axial position of the spool along the bore, whereby fluids can pass between the spool and the valve housing. The passageway of one of the spool or the valve housing includes a first groove which extends parallel to the axis, but not completely, circumferentially about said one of the spool or the valve housing. The passageway of another of the spool or the valve housing includes a second groove which extends circumferentially about said another of the spool or the valve housing.
The invention offers significant advantages compared to the prior art. It allows the spool valve to be used in applications where a sudden flow of fluid, or a sudden cessation in the flow, as occurs when a conventional spool valve opens and closes, would be disadvantageous. In particular, the valve is advantageous for use on marine steering systems. It provides a combination steering actuator and spool valve connected to the tiller of the marine craft. Such a combination of an actuator and spool valve, according to the invention, effectively dampens drive oscillations without the necessity of centering springs, external dampers or chamfers on conventional annular spool grooves as required by some prior art systems. Thus the number of components is significantly reduced and the system is overall more economical and reliable.